Overview

What are the physical and biological processes that determine large scale spatial gradients in biodiversity? How do species and communities respond to climate change and other anthropogenic impacts and what are the ecological and evolutionary consequences of such responses? These and related questions form the focus of my research. My research is interdisciplinary in nature and combines the temporal perspective afforded by the fossil record and historical samples with ecological and genetic information from living species and populations. I primarily work with coastal marine species but recently have also initiated work on terrestrial gastropods, a group highly vulnerable to climate change, urbanization and habitat loss. Some of the main areas of my research are briefly summarized below.

Origin and maintenance of the Latitudinal Diversity gradient

The latitudinal diversity gradient (LDG) - a dramatic increase in the richness of species and higher taxa from the poles to the tropics - is a global biodiversity pattern shared by both marine and terrestrial ecosystems. Understanding the processes responsible for the origin and maintenance of the LDG has been a focus of biology for over two centuries and is essential for formulating effective management and conservation strategies. Yet, despite considerable progress, the environmental and biological drivers of the LDG remain poorly understood; two dozen major hypotheses have been proposed to explain this pattern, but none has gained general acceptance. For a number of years now, I have been involved in testing existing hypotheses about the origin and maintenance of the LDG and also in developing new models. In this ongoing work we are attempting to understand the evolutionary processes that generate the LDG as well as the ecological ones that maintain such gradients.

Biotic effects of climate change

Climate is widely recognized as one of the major determinants of spatial distributions of species but predicting how species and ecosystems are likely to respond to anthropogenic warming remains a major challenge for biology. My work on the biotic effects of climate change focuses on both ecological (e.g. species range shifts and changes in community compositions) and evolutionary effects. The glacial-interglacial cycles during the late Pleistocene provide a set of natural experiments that can be used to investigate biotic responses to large scale changes in climate. Using a combination of the Pleistocene and Holocene record of living species, molecular markers, geochemical data and phenotypic measurements we are investigating how marine molluscan species responded to past changes in climate. The ultimate goal here is to use this information, in combination with ecological and functional data, to identify species that are likely to be affected by future warming (or conversely those that are likely to be resilient).

Ocean acidification

Changes in calcium carbonate saturation state of the world oceans due to anthropogenic CO2 emissions potentially represent one of the major threats to the future of marine biodiversity. Short term laboratory experiments have shown that individuals of many species with calcium carbonate shells are potentially vulnerable to ocean acidification but such experiments ignore the role of local adaptation and other population-level processes. Because the carbonate saturation state of the oceans has fluctuated substantially over geologic time, the fossil record can provide critical insights into how individual species and communities react to changing saturation states. Similarly, the archeological record and specimens in museum collections also give us a pre-industrial baseline for investigating this issue. We are investigating how select species of coastal northeastern Pacific mollusks (including some that are commercially important) respond to ocean acidification by comparing calcification rates of Plio-Pleistocene, archeological and historical specimens with those of living individuals and using geochemical proxies to infer changes in temperature and ocean pH. In addition, we have initiated microcosm experiments using some of the same species to explore whether the results of such experiments are consistent with those using the comparative approach mentioned above.

Conservation of coastal ecosystems

Harvesting of coastal marine invertebrates for food and other use is widespread all over the world. Such harvesting is almost always size-selective, preferentially targeting large individuals. However, little quantitative data exist about the biological consequences of such exploitation, largely due to the lack of baseline information against which to compare present day patterns. In most cases we do not know how harvesting impacts life histories and phenotypic traits, whether it leads to extensive local extinctions of the targeted species or changes local abundances and/or populations structures of species. From an evolutionary perspective, preferential loss of the largest individuals in a population represents a novel selective force, something species are unlikely to have experienced in their evolutionary past. So how such harvesting practices will shape future evolutionary trajectories of many species remains an important question. In addition, we also know little about how harvesting affects macroecological relationships or biogeographic patterns. We are addressing these and related issues using coastal marine molluscan species as a model system. See the CBRISC site for more information about this work.